1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the power level of a radio frequency signal being sent to an antenna of a mobile transmitter such as a mobile phone. The detected power level is used in an automatic gain control circuit.
2. Description of the Related Art
Power detection of radio frequency (RF) signals in a known Digital Advanced Mobile Phone System (DAMPS) may be implemented by taking a plurality of samples of the RF signals from a signal envelope and averaging the samples using Digital Signal Processing (DSP) to eliminate variations in the signal envelope. Since the variations in the envelopes of the modulated RF signals are not that large in DAMPS, the samples may be randomly taken to gain a useful estimate of the power level of the RF signals.
In other modulated RF signals such as Enhanced Data Rates for GSM Evolution (EDGE) modulated signals, the variations in the signal envelopes are much greater, which makes it more difficult to achieve a useful estimate of the power level of the RF signals using random samples. Averaging on the analog side may be employed to reduce the envelope variations, after which the above described sampling may be used. However, the EDGE modulated signal may be a multi-slot signal, in which case there is only a 30 microsecond gap between consecutive time slots, and the power difference between the slots may be as great as 20–30 dB. It is therefore difficult to configure and deploy a low-pass filter with a time constant that is small enough to ensure fast discharge and that also has a sufficiently low corner frequency to minimize error in the detected power.